Ask the Mechanic: Why does my car require premium fuel?

This question is not as complex as one might think.
The main reason that a turbo-charged or super-charged engine requires premium grade fuel is for its higher octane value. This is to stop detonation in the cylinders by artificially raising the compression ratio in the engine by forced induction.
Now that we have that concept out of the way, there are a few more things that we can add to the equation.
Most newer vehicles that have forced induction also have knock (ping) sensors and fuel control sensors that perform adjustments to compensate for fuel quality.
While the engine will compensate for poor fuel quality, the performance will suffer along with fuel economy.
So, the bottom line is, use the fuel that is recommended by the manufacturer to get the best fuel economy possible.
Cal Adamson is the service manager for Maita Ford Mercury, 1650 Highway 49, Auburn. He can be reached at (530) 823-6591.
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C/O Andrew DiLuccia
1030 High Street
Auburn CA, 95604
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